Thermionic tube



Aug. 21, 1934.

P. F. SCOFIIELD THERMIONIC TUBE Filed July 18, 1932 INVENTOR H/L/P F SCOF/ELD.

/f. ATTORNEY Patented Aug. 21, 1934 UNITED STATES THERNHQNIC TUBE Philip F. Scofield, Palo Alto, Calif.,

assignor to Heintz & Kaufman, Ltd., San Francisco, Calif., a corporation of Nevada Application July 18, 1932, Serial No. 623,114 2 Claims. (01. 250-275) My invention relates to a thermionic tube having a variable amplification factor and more particularly to such a tube in which the cathode is unequally spaced from the control electrode, and positioned between the control electrode and the anode.

Among the objects of my invention are: To provide a thermionic tube having a variable amplification factor or mu-factor; to provide a variable mu tube of simple and economical construction; to provide a thermionic tube having a mufactor which varies from point to point of the cathode area; and to provide a variable mu tube designed for the elimination of distortion in radio receiving sets.

Other objects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of my inven- 20 tion herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing:

Figure 1 is a view, partly in section and partly in elevation, of a vacuum tube embodying this invention.

Figure 2 is a cross sectional view of the tube, taken on the plane indicated by the line 2-2 in Figure 1.

Figure 3 is a longitudinal sectional view of the electrodes only, taken at right angles to the plane of section of Figure l as indicated by the line 3-3 in Figure 2.

In broad terms my invention comprises a thermionic tube having an anode and control 3 electrode, with a cathode inserted between the two electrodes and so positioned that the various portions of the cathode are unequally spaced from either the anode or control electrode. A mufactor is then obtained in operation which varies from point to point of the cathode area.

A preferred embodiment of my invention is shown in the drawing. A bulb 1 is provided with a reentrant stem 2 in the usual manner. A pinch 4 supports an anode 5 on anode leads 6, a control electrode 7 on control leads 9, and a filamentary cathode 10 on cathode leads 11, the electrodes preferably being welded to the leads. The anode and control electrode are of plate form and usually identical in size and shape, being formed from nickel or tantalum. Flanges l2 stiffen their longitudinal edges.

Welded to the top portion of anode and control electrode are bridge supports 14 fitting into holes in a spring bridge 15 of insulating material such as isolantite or lava, which connects the two plate electrodes. Parallel alignment of the two electrodes is easily obtained by adjustment of the bridge supports 14.

A spring hole 16 is drilled on an angle through the bridge near the upper edge of the control electrode through which a filament support hook 1'7 is passed and fastened to a filament spring 18 by a weld 19. a

The filamentary cathode, being in the form of an inverted V, is engaged at its apex 20 in the filament hook 17 and is maintained under slight tension by the spring. This cathode filament is adjusted to be angularly disposed with respect to the control electrode, in this case having the apex 20 close to the control electrode and its basal portion several times as far away.

Using the same general construction several variations giving the same result will be apparent. For example, the apex may be made the distant portion, or, the cathode may be made parallel to the anode and the control electrode tilted to obtain unequal spacing. I also contemplate curving the control'electrode to obtain departure from the results obtained by angular relationship.

After the desire spacing adjustments are made the tube is pumped, sealed and tested in the customary manner.

The tube is then provided with a base 21. Anode seal section 22, control seal section 23 and cathode seal sections 24 being fused in the pinch, are extended to enter the contact prongs 25, carried by the base, and are fastened to them by the customary solder 26. Any desired order may be used but I prefer the arrangement now standard in the art.

In tubes built in the manner described, the

amplification will be highest at the point where the cathode closest approaches the control electrode, and lowest at the point of greatest spacing. The advantages of a high amplification factor are retained at normal voltages, while at high biases, the low distortion characteristics of a low mu tube are automatically obtained.

While my invention is described as being adapted to three-electrode tubes, it is obvious that the same results will be obtained when used in conjunction with tubes having several control, accelerating or shielding electrodes.

I claim:

1. A thermionic tube comprising a plurality of electrodes positioned in parallel planes, a cathode interposed between two of said elec-' trodes, the plane of said cathode being at an angle to the planes of said electrodes.

2. A thermionic tube having an anode and a control electrode positioned in parallel planes, a filamentary cathode having an apex and a base defining a plane, the plane of said cathode being at an angle to the planes of said anode and said control electrode, the apex of said cathode being closer to said control electrode than said base.

PHILIP F. SCOFIELD. 

